Structural trusses are very useful in a wide variety of situations. They can be used vertically, horizontally or in any other possible orientation. They generally include an elongated framework having three or more spaced-apart tubes extending in the lengthwise direction. The longitudinal tubes are rigidly interconnected to one another using a network of intervening members.
In most implementations, at least one end of each structural truss needs to be connected to an adjacent element in a construction assembly. The adjacent element can be a supporting structure or another structural truss. For instance, two adjacent structural trusses can be connected directly end-to-end or through another element. Various factors can impose limitations to the length of a structural truss and, for instance, it may be required and/or more desirable to attach two or more smaller structural trusses instead of using a single but longer structural truss. A very long structural truss can create complications in terms of handling and transportation, for example. Using smaller lengths of structural trusses assembled together is generally desirable.
In use, bending moment in a structural truss set at the horizontal is carried by tension or compression in the chords and the shear force is carried by the diagonals. The purpose of a connection is to transfer the bending moment and shear force from one structural truss or module to the next. The connection must also be stable.
Connecting one end of a structural truss to an adjacent element create some challenges, especially when welding is involved. The known connector arrangements have used parts such as small plates or gussets welded to the end face of the framework so as to provide a supporting interface for fasteners, in particular removable fasteners such as sets of bolts, nuts and washers. The welding process typically creates heat affected zones. These zones are generally extending up to one inch from the weld beads. The metal in the heat affected zones is more ductile than before the welding and the allowable stress in the heat affected zones is reduced by a substantial factor. Using larger tubes and/or plates can compensate for the heat affected zones but this adds weight and costs. It also reduces the space available for the fasteners. The fasteners must be located as close as possible to the corners of the structural truss to increase strength.
FIG. 22 illustrates an example of a structural truss 500 as found in the prior art. This structural truss 500 has end plates 502 welded to four interconnected tubes forming the end of the framework 504. The end plates 502 include holes made through their thickness to receive the shank of the connecting bolts. When connecting two of these structural trusses 500 together, the head of the bolts will be on the inner side of the end plates 502 of one structural truss 500, and the opposite nuts will be on the inner side of the end plates 502 of the other structural truss. Annular washers are provided between the head of the bolts and the back side surface of the end plates to distribute the forces on a wider area. Annular washers are also used between the nuts and the back side surface of the opposite end plates 502 for the same reasons. Moreover, since the end frame is also welded onto the framework, this part of the structural truss also includes heat affected zones.
The typical route which the retaining forces in such arrangement is as follows:
chord—weld—end frame—weld—end plate—washer—bolt—nut—washer—end plate—weld—end frame—weld—chord.
The bolts, nuts and/or washers transmit the load into the end plates 502, which induce a considerable amount of local stress and deformation. Since the distance between the neutral axis of the bolt and the chords are distanced depending of the industry standard of holes position, it is often not possible to use oversized washers in order to distribute the load on a wider area in order to lower the mechanical stress on the end plates 502 around the holes. This can significantly reduce the end plate capacity. The use of larger tubes at the end frame to compensate for the head affected zones can force designers to move the fastener holes further away from the corners, which again can reduce the load bearing capacity.
Clearly, room for improvements exists in this area.